Car seat pads are formed by molded polyurethane foam (for example, Japanese Unexamined Patent Application Publication No. 2000-37739).
Some car seat pads have backboards on the bottom surfaces thereof. FIG. 3 illustrates a method for forming a seat pad having a backboard.
Referring to FIG. 3a, a mold 1 includes a bowl 2 and lids 3 and 4. A polyurethane precursor solution R is poured into the bowl 2. The lids 3 and 4 are closed to the bowl 2 before polyurethane reaction by heating. Referring to FIG. 3b, a molded foam 5A is formed after the expansion and is released from the mold 1. Referring to FIG. 3c, a seat pad is completed by attaching a backboard 6 to the molded foam 5A. In FIG. 3c, the seat pad is illustrated upside down with respect to the orientation for installation in a vehicle.
An edge of the backboard 6 engages with a recessed step 7 formed in the bottom surface of the molded foam 5A (in the top surface in the drawings). Numeral 5a denotes an external corner left after the step 7 is formed. The upper mold portion 4 has a projecting step 8 for forming the recessed step 7. The projecting step 8 is L-shaped in cross section.
For the molded foam 5A shown in FIGS. 3a to 3c, the projecting step 8 of the lid 4 makes it difficult to sufficiently fill an internal corner 8a with expanding polyurethane. The projecting step 8 thus tends to cause air to be left around the external corner 5a of the molded foam 5A, which is formed by the internal corner 8a of the lid 4.